The present specification relates to polymeric water retention agents which contain no free acrylamide and are based on vinylic sulfonic acids and to their use.
Drilling fluids are used very generally in the processes referred to as rotary processes for drilling for oil and gas These processes are based on the rotation of the drillstring which has at its end the drill bit. The bit drills through the rock and as it does so forms what are known as drillings, which accumulate as drilling progresses. Pumped through the hollow drillstring is a drilling fluid which emerges at the drill bit and flows through the annular space between drill drain and rock formation back to the surface, while fulfilling the following principal functions:
a) lubricating and cooling the drill bit
b) suspending and discharging the drillings
c) stabilizing the borehole against the formation pressure
Formations containing oil and gas are generally composed of porous rock strata, so that the production rate of the oil or gas is heavily dependent on the permeability of the respective formations. When drilling through such porous structures it is therefore desirable to use a drilling fluid which prevents the penetration of sizeable amounts of liquid or solids into these strata, prevents blockage of the pores, and generally prevents any deterioration in the permeability for oil or gas, this being referred to as filtrate control.
Filtrate control is also of great importance, however, in the cementation of a borehole, where a casing is introduced into the borehole and a cement slurry is pumped into the cavity between the formation and the casing. In this case the cement slurry is subjected to high hydrostatic pressures, with the consequence that water may be pressed from the cement slurry into the formation. This results not only in the described damage to the formation but also in a loss of the water which is needed for complete setting of the cement.
The prior art has disclosed a variety of additions to drilling fluids or cement slurries:
For instance, U.S. Pat. No. 4,309,523 discloses a high-temperature-stable drilling fluid additive which is composed preferably of 2-acrylamido-2-methyl-propanesulfonic acid (AMPS), N-vinylalkylamide and acrylamide terpolymers.
In accordance with U.S. Pat. No. 3,898,037, AMPS copolymers are used as dispersants for insoluble particles in aqueous systems, with the comonomers listed including itaconic acid and maleic acid.
In order to control fluid loss, the EP patent 572 697, for water-based drilling muds, provides polymeric additives which are composed of from 10 to 90% by weight of AMPS, from 1 to 60% by weight of alkylacrylamide, from 1 to 60% by weight of various nonionic, xcex1-ethylenically unsaturated monomers and from 1 to 60% by weight of carboxyl-containing monomers, such as maleic acid, for example.
U.S. Pat. No. 4,741,843 describes terpolymers of AMPS, nonionic, xcex1-ethylenically unsaturated monomers (e.g., acrylamide) and unsaturated polybasic acids, which are used as fluid loss additives in particular for calcium-containing drilling fluids.
WO 00/09625 teaches the use of an additive which stabilizes clay slate and comprises maleic acid polyethylene glycol semiester-styrene copolymer. U.S. Pat. No. 3,525,688, finally, discloses a drilling fluid to which polyethylene glycol is added in order to control the rheological properties. These two last-mentioned documents do not indicate any connection with filtrate-reducing properties of the additives employed.
Disadvantages of all of these known additives, among other things with filtrate-reducing properties, are their carcinogenicity when they contain fractions of free acrylamides or else their sometimes deficient stability under the usually extreme conditions, especially those of drilling.
As a result of these serious disadvantages of the prior art, the object which has emerged for the present invention is to provide water retention agents based on vinylic sulfonic acids, which contain no free acrylamide and are suitable for drilling fluids and cement slurries, which greatly reduce the filtrate loss from drilling fluids even at temperatures above 200xc2x0 F., at very high pressures and electrolyte concentrations, and which, furthermore, contain no carcinogenic monomers.
The term xe2x80x9cfree acrylamidexe2x80x9d here refers to all fractions of the compound having the CAS No. [79-06-1]. Acrylamide comprising compounds such as 2-acrylamido-2-methylpropanesulfonic acid (AMPS), for example, or other acrylamide derivatives are explicitly not covered by this definition.
Said object has been achieved with a corresponding water retention agent composed of
1) xe2x89xa730 mol % of component A which is selected from the group consisting of
a) vinylic substituted sulfonic acid of the series 2-acrylamido-2-methylpropanesulfonic acid (AMPS), vinylsulfonic acid, methallylsulfonic acid or styrenesulfonic acid, salts thereof with a valence of at least 1, or mixtures thereof, or
b) a divalent salt of homopolymers or copolymers of a vinylic substituted sulfonic acid of the series 2-acrylamido-2-methylpropanesulfonic acid (AMPS), vinylsulfonic acid, methallylsulfonic acid or styrenesulfonic acid or mixtures thereof, and in case 1a)
2) component B), composed of
a) from 4.99 to 60 mol % of an unsaturated, polybasic, cis-positioned carboxylic acid monomer and
b) from 0.01 to 10 mol % of a monomer having a polyalkylene oxide side chain which contains from 1 to 120 repeating units of the alkylene oxide.
With the polymers of the present invention it has surprisingly been found that they develop their highly pronounced water retention effect as fluid loss additives, in particular in drilling applications, even under very extreme conditions, with consistent quality. In this context it is worth mentioning in particular that the polymers of the invention are able to develop their thickening effect even in drilling fluids which comprise alkali metal formate weighting agents. This is all the more surprising on account of the fact that such drilling fluids were hitherto regarded as being virtually impossible to thicken.
It has also been found, again surprisingly, that when salt forms of component A are employed the counterion apparently has a very positive influence on the water retention effect.
For this reason not least the present invention provides on the one hand that when the monomer 1a) is present in salt form said salt comprises as its cation one from the series Na+, K+, Ca2+, Mg2+, Zn2+, Ba2+ and/or Fe2+. On the other hand, the sulfonic acids in the form of their homopolymers and/or copolymers may comprise divalent salt counterions, preferably Ca2+, Mg2+, Zn2+, Ba2+, and Fe2+.
In comparison with, for example, sodium, potassium and also ammonium, in other words monovalent counterions, it was possible to lower the fluid loss levels by approximately 50% in respect of component 1b), for example, with magnesium and calcium counterions.
The anions here do not have such a critical role, and so it is possible easily to employ the otherwise customary carbonates, sulfates, hydroxides or else chlorides. There is likewise no need to stress the possibility that the vinylic sulfonic acids co-claimed as component A can be substituted by organic radicals, such as C1-4 alkyl or suitable aromatics, for example.
In addition to the claimed variant wherein the homopolymer and/or copolymer 1b) of the invention further comprises up to 70 mol % of a monovalent salt and in particular of a sodium, potassium and/or ammonium salt of vinylsulfonic acid, styrenesulfonic acid, methallylsulfonic acid and/or AMPS, the present invention also provides the possibility that the homopolymer and/or copolymer 1b) comprises up to 50 mol % of at least one unsaturated, polybasic, cis-positioned carboxylic acid compound, such as maleic acid, maleic anhydride (MSA), citraconic acid or itaconic acid, for example, as comonomer. With these variants a further surprising effect, namely a synergistic effect, has been found: Na-AMPS-MSA copolymers, for example, exhibit a fluid loss effect which is comparable with that of the Na-AMPS homopolymer. With the polymers 1b), including the inventive polymers 1b), in the form of Ca-AMPS-MSA copolymers, for example, the fluid loss level is drastically reduced to only ⅓.
With respect to the monomer 2a), maleic acid, maleic anhydride, citraconic acid, itaconic acid and mixtures thereof are regarded as preferred polybasic, cis-positioned acids.
As with component A, in the case of monomer 2a) as well particularly suitable monomers are those which are present at least in part in the form of a salt of an at least monovalent cation of the series Na+, K+, Ca2+, Mg2+, Zn2+, Ba2+ and/or Fe2+.
The polyalkylene oxide side chain of the monomer 2b), which is required to contain between 1 and 120 repeating units of the alkylene oxide, particularly in the form of a polyethylene oxide, polypropylene oxide, polytetrahydrofuran or mixtures thereof, may preferably be in the form of (meth)acrylate, (meth)acrylamide, vinyl ester, monoester or amide of maleic acid in the polymer backbone. In this respect the invention also provides that the polyalkylene oxide side chain is preferably either hydroxy-terminated or methoxy-terminated.
Overall, among the polymeric agents claimed, those which have been found particularly advantageous are those whose molar weight lies between 10 000 and 3 000 000 g/mol, with variants having a molar weight of between 75 000 and 1 000 000 g/mol being regarded as especially preferred.
The polymeric water retention agents of the present invention composed of components Ab) or Aa) and B may in principle be prepared by means of all conventional polymerization processes; however, preference is given to those agents which can be prepared by solution, precipitation, gel, emulsion or suspension polymerization.
In addition to the polymeric, acrylamide-free water retention agent itself, the present invention also claims its use in drilling for oil, gas and water, particular preference being given to its use as an additive to drilling fluids, completion fluids, workover fluids and/or in cement slurries.
A particular advantage when using the polymers of the invention can be achieved when they are used in drilling media with high electrolyte contents of between 50 ppm and their saturation point and/or at temperatures of more than 200xc2x0 F. and with particular preference more than 400xc2x0 F.
A further advantage of the agent of the invention is considered its use for drilling fluids, completion fluids and/or workover fluids which comprise formates and especially alkali metal formates, and this is likewise taken into account by the present invention.
Finally, the present invention also claims the use of the agents as water retention agents in the construction sector, especially for plasters, tile adhesives, and leveling compounds.
In summary, the advantages of the water retention agent of the invention are regarded as being that it develops a very pronounced water retention effect as a fluid loss additive for drilling fluids, completion and workover fluids and also cement slurries and generally in the construction sector, even under very extreme conditions, with consistent quality and that it maintains in particular the significantly improved filtrate-reducing properties even under otherwise unfavorable drilling conditions such as high temperatures and/or high pressures and/or heightened electrolyte levels and in the presence of formates over the entire drilling system. In addition, the claimed agent is free from monomers which have proven carcinogenic, such as free acrylamides, for example.
These advantages of the present invention are illustrated by the following examples.